Short-range order in strongly correlated Fermi systems

The role of short-range order (SRO) in strongly correlated metallic systems is discussed. Magnetic neutron scattering experiments show that SRO is a universal property of such systems. Different theoretical approaches to the analysis of SRO are considered. Microscopic models based on infinite-dimensional lattice solutions (the Monte Carlo variational technique, the 1/D+1/D² expansion for the Gutzwiller trial wave function, and the dynamical mean-field theory) do not correctly describe SRO in strongly correlated systems. A variational theory of SRO in Fermi systems is presented in which, in addition to Gutzwiller's variational parameter, a set of new parameters describing nonlocal short-range correlations is used.